rp0123

Hopefully, the block on AI pit maneuvering burrito vans will be removed for the enhanced version. 
Also the anti pit maneuver traction that lspdfr applies to pursuit suspect's vehicle. 
 
Clarification edit: LSPDFR backup AI seems to be blocked from being able to use tactics on vehicle with big in strModelFlags.  They can't do pit maneuvers on burrito van, but if the flag is removed, then AI can pit them. 
 
Also it takes abnormal amount of force to pit pursuit suspect's vehicle, that only AI backup with cheat force could do it or have to use the plugin.
 

Even setting Chase.DisableTrafficDensityAdjustments to true, traffic spawn is still diminished with LSPDFR.
Especially affected if added DLC cars into popgroups. 
 

There are critical bugs with automatic roadblock plugin and development seems to have ceased. 

What do you mean SET_PED_COMBAT_ATTRIBUTES does not have a leave vehicle flag available? Set flag 3 to 0 and it should prevent them from leaving.

Maybe try suspect.IsCollisionEnabled;

Try config flag 107 (CPED_CONFIG_FLAG_DontActivateRagdollFromBulletImpact).

I've looked into the decompiled code for the Paleto heist and this is everything I found regarding ragdoll:
 
SET_RAGDOLL_BLOCKING_FLAGS(ped, 32768)
 
SET_PED_CAN_RAGDOLL_FROM_PLAYER_IMPACT(ped, false)
 
Ped.CanRagdoll was also used but you already tried that