diff --git a/countess/core/parameters.py b/countess/core/parameters.py
index 77d48c1..7302fb7 100644
--- a/countess/core/parameters.py
+++ b/countess/core/parameters.py
@@ -297,7 +297,7 @@ def get_file_hash(self):
                 try:
                     # Python 3.11
                     digest = hashlib.file_digest(file, PARAM_DIGEST_HASH)
-                except AttributeError:
+                except AttributeError:  # pragma: no cover
                     digest = hashlib.new(PARAM_DIGEST_HASH)
                     while True:
                         data = file.read()
@@ -725,8 +725,6 @@ def del_row(self, position: int):
         assert 0 <= position < len(self.params)
 
         self.params.pop(position)
-        if len(self.params) < self.min_size:
-            self.params.append(self.param.copy())
         self.relabel()
 
     def del_subparam(self, param: BaseParam):
@@ -734,6 +732,8 @@ def del_subparam(self, param: BaseParam):
         self.relabel()
 
     def relabel(self):
+        while len(self.params) < self.min_size:
+            self.params.append(self.param.copy())
         for n, param in enumerate(self.params):
             param.label = self.param.label + f" {n+1}"
 
@@ -744,8 +744,6 @@ def __len__(self):
         return len(self.params)
 
     def __getitem__(self, key):
-        while len(self.params) <= int(key):
-            self.add_row()
         return self.params[int(key)]
 
     def __setitem__(self, key, value):
@@ -785,7 +783,7 @@ def set_parameter(self, key: str, value: Union[bool, int, float, str], base_dir:
                 assert isinstance(param, (HasSubParametersMixin, ArrayParam))
                 param.set_parameter(subkey, value, base_dir)
 
-        else:
+        elif self.max_size is None or int(key) < self.max_size:
             while int(key) >= len(self.params):
                 self.params.append(self.param.copy())
             param = self.params[int(key)]
@@ -810,14 +808,14 @@ def get_parameters(self, key, base_dir="."):
 
     def set_column_choices(self, choices):
         params_by_label = {p.label: p for p in self.params}
-        self.params = [None] * len(choices)
-        for num, name in enumerate(choices):
-            if name in params_by_label:
-                self.params[num] = params_by_label[name]
+        self.params = []
+        for label in choices:
+            if label in params_by_label:
+                self.params.append(params_by_label[label])
             else:
-                self.params[num] = self.param.copy()
-                self.params[num].label = name
-            self.params[num].set_column_choices(choices)
+                self.params.append(self.param.copy())
+                self.params[-1].label = label
+        super().set_column_choices(choices)
 
     def get_column_params(self):
         for p in self.params:
diff --git a/tests/test_parameters.py b/tests/test_parameters.py
index 5eea1ff..eac481d 100644
--- a/tests/test_parameters.py
+++ b/tests/test_parameters.py
@@ -1,5 +1,5 @@
 import io
-from unittest.mock import mock_open, patch
+from unittest.mock import patch
 
 import pandas as pd
 import pytest
@@ -15,10 +15,12 @@
     ColumnOrNoneChoiceParam,
     DataTypeChoiceParam,
     DataTypeOrNoneChoiceParam,
+    FileArrayParam,
     FileParam,
     FloatParam,
     IntegerParam,
     MultiParam,
+    PerColumnArrayParam,
     ScalarParam,
     StringCharacterSetParam,
     StringParam,
@@ -108,6 +110,7 @@ def test_multiparam():
     )
 
     assert "foo" in mp
+    assert sorted(mp.keys()) == ["bar", "foo"]
 
     mp["foo"] = "hello"
     assert mp.foo == "hello"
@@ -123,6 +126,9 @@ def test_multiparam():
     mp.set_parameter("foo._label", "fnord")
     assert mp["foo"].label == "fnord"
 
+    with pytest.raises(AttributeError):
+        assert mp.fnord
+
 
 def test_scsp():
     pp = StringCharacterSetParam("x", "hello", character_set=set("HelO"))
@@ -277,6 +283,23 @@ def dummy(*_, **__):
     fp.value = "/foo/bar/baz"
     assert fp.get_parameters("fnord", "/foo") == [("fnord", "bar/baz")]
 
+    assert fp.get_parameters("fnord", "") == [("fnord", "/foo/bar/baz")]
+
+    fp.value = ""
+    assert fp.get_parameters("fnord", "") == [("fnord", None)]
+
+
+def test_filearrayparam():
+    ap1 = FileArrayParam("x", param=FileParam("Y"))
+    assert ap1.find_fileparam().label == "Y"
+
+    ap2 = FileArrayParam("x", param=MultiParam("Y", params={"z": FileParam("Z")}))
+    assert ap2.find_fileparam().label == "Z"
+
+    with pytest.raises(TypeError):
+        ap0 = FileArrayParam("x", param=IntegerParam("Y"))
+        ap0.find_fileparam()
+
 
 def test_arrayparam_minmax():
     pp = IntegerParam("x")
@@ -295,6 +318,25 @@ def test_arrayparam_minmax():
     ap.del_row(1)
     assert len(ap) == 2
 
-    # FIX minimum and maximum constraints!
-    # ap.del_subparam(ap[1])
-    # assert len(ap) == 2
+    assert ap[1] in ap
+    ap.del_subparam(ap[1])
+    assert len(ap) == 2
+
+    ap[0] = 7
+    assert ap[0].value == 7
+
+
+def test_pcap():
+    pp = IntegerParam("x")
+    ap = PerColumnArrayParam("y", param=pp)
+
+    ap.set_column_choices(["a", "b", "c"])
+    assert len(ap) == 3
+    apa, apb, apc = list(ap)
+
+    ap.set_column_choices(["c", "d", "b", "a"])
+    assert len(ap) == 4
+    assert ap[0] is apc
+    assert ap[2] is apb
+    assert ap[3] is apa
+    assert ap[1] is not apb