Hello Kaushik,
Normally this strategy of EM and heap memory consumption is guided by parameters ES/TABLE. In my opinion, if EM is getting used first for dialog and BGD processes both, this should be normal.
FIrst em/roll_extension will be used up and then if heaplimit is reached, WP can take up till heap_area_dia or non_dia depending if other WPs are already not comsuming heap.
Let me know if you have some other question, thanks.
Regars,
Ankit