I might even be mistaken about perks being in tmap chests. They are in paragon chests for sure but I really don't think I've done a tmap since their addition. It is a relatively new addition, sometime last year. In my experience the chance of a perk in a chest is about 15% The frags you've just had bad luck on I guess. Higher level maps don't seen to make much of a difference from what I've heard it's less than 5%, one in 30-50 maps. Again just what I've heard.