if you make the sturmtiger's attack range lke the ST of coh 2 , it will not break the BKs balance. this is suitable as a reward unit for the stupa.
making the grille another doc specific unit in bk.
as long as it must lockdown first to fire and has a 150munition cost per shot and a large cooldown
17 pdr using APVPs shells can quickly dispatch it from a distance. also 76mm AT guns using APCR
flanking it is also easy.