it is always difficult to apply the vocabulary from one vendor to another. In ALU, hysteresis is a term that only appear in idle mode, while it is also a HO parameter in other systems.
Anyway, specifically for ALU, here is what you should do :
* from cell A to cell B:
HO_MARGIN(A,B) = 8dB
* from cell B to cell A
HO_MARGIN(B,A) = 5dB (= default)
* in cell A
PING_PONG_HCP = 20s
A_PBGT_HO = 12 SACCH
are cell B and A in the same frequency band (900MHz both of them ?)
If above settings don’t work perfectly, try to increase (slowly !)
1) the ping pong hcp by +20s
2) the HO_MARGIN(A,B) by +2dB and the A_PBGT_HO by +2SACCH.
Beware of emergency HO ratio in the cell A, with the solution 2, as it is getting now more difficult to get out of cell A.