Hi Solarspace, The BIR Chicken Tikka is cooked using the tandoor, and yes the marinade is fairly runny, at home people attempting to make their own marinade for tikka use greek style yougurt which is fine but needs to be played with a little to loosen before using, also adding the other ingredients which will thicken it furthur , using a home grill and lying the tikka flat to cook does not help to evenly distribute the marinade, standing upright in the tandoor on squewers with the required heat needed does allow the marinade to drizzle evenly over the chicken coating it evenly, i have witnessed this in my good friends tandoor using my marinade, we have had great results, you may want to save some pennies and buy yourself a tandoor, also my nann bread takes on a whole new taste and texture when tandoor cooked rather than grilled.

Hope it helps you a little, if you want my marinade recipe i will gladly let you have it.