For tie only in Nth position, let me share a POC I did in BO 4.1 SP3 :
Let's assume the initial data grid as :
Dimension
|
Measure
|
|---|---|
A
|
10
|
B
|
9
|
C
|
8
|
D
|
7
|
E
|
5
|
F
|
5
|
G
|
5
|
H
|
5
|
I
|
2
|
Create variables as :
v_Rank ="Rank"+Rank([Measure])
(Assuming top 5) v_Top N =If(Count([v_Rank] Where (Rank([Measure])<=5) In ([Dimension]);All)In Block >5;4;5)
v_FilterFlag =If(Rank([Measure])<=[v_Top N];1;0)
Now create a block level filter as : v_FilterFlag Equal To 1
You are done 
Dimension
|
Measure
|
|---|---|
A
|
10
|
B
|
9
|
C
|
8
|
D
|
7
|
Now, if I change the value at 5th position to remove the tie, we get:
Dimension
|
Measure
|
|---|---|
A
|
10
|
B
|
9
|
C
|
8
|
D
|
7
|
E
|
6
|