Welcome aboard Acrabat.Don't worry I actually lurked on here for a couple of years before posting!!
I'm always intrigued in any tikka marinades that doesn't actually use yoghurt as an ingredient.Abdul certainly used it on my home lessons,I saw a chef make a marinade using yoghurt on my T/A lesson and one of my local T/A's leave their empty catering tubs of the stuff around their back.I'm sure Heston actually did an experiment and found that yoghurt does improve the texture of meat for certain.However I've always found that my marinade was a bit too thick and cake like around the meat.The tikka I buy round here seems to have a very thin marinade but it's always penetrated deep into the chicken.
A few people have mentioned that milk should be added to the yoghurt to thin it down.Funny enough my wife used to go out with guy who was a delivery driver in a restaurant.She would spend hours in the kitchen talking to the chefs,she still remembers that the chef used to get through loads of cartons of milk in a week.Could he have been using this in his marinade?? Hopefully Az can give us his take on tikka marinade and whether he has ever used milk.