Changing TAdvStringGrid FixedFont size in runtime mode does not work

I can change font size, but if I set AGrid.FixedFont.Size in runtime (in design time it works ok), notinhg changes. I checked in and I tried it with UseFixedFont True and False.

Cannot be reproduced:

Thank you for quick checking it. You are right. After your answer I have made additional tests. The fixed font can not be set, if cells are merged or cells have alignment assigned to it:
AdvStringGrid1.MergeCells (3, 0, 2, 1);
AdvStringGrid1.G.Alignments[0,1] := taCenter;

The first case can be resolved by setting Font size in method OnGetCellColor and second one can be resolved by method OnGetCellAlignment. Thank you!

When you merge cells, the cell properties take over from the global settings.
Change the cell properties of the top left cell for merged cells via properties like grid.FontSizes[col,row]: integer, grid.Alignments[col,row]: TAlignment;