OK, I gave your code a run - took the risk and as you say, there was no gap. Puzzling.
Mine application still shows a gap. I have had a look at all Form attributes on both and there does not seem to be anything that could cause a discrepancy.
I have attached a screen shot showing the gap.
The code is these forms is simple :-
Form 1
Private Sub Form_Load()
' Left, Top, Width, Height
Me.Move 3000, 0, , 2500
End Sub
Form 2
Private Sub Form_Load()
' Left, Top, Width, Height
Me.Move 3000, [Form_F1].WindowTop + [Form_F1].WindowHeight, , 3000
End Sub
You will also notice that Form 2 is slightly to the left of Form 1. This is because I made Form 1 with Border Dialog and Form 2 with Border None
I am sure I will get to the bottom of this somehow, but can't figure it out yet.
As I say, I have a workaround, so don't waste your time on this.
It is very strange.