I think you should discuss the questions you have raised on PPRuNe with your training officers and accept what they say.
The correct attitude is trust, but check. Never, EVER, be discouraged from asking someone to justify their opinion even if they are more experienced than you or are in a position of authority (such as OJTI or UCE). You do not have to simply accept anything, you are entitled to an explanation to aid your understanding. To be good at ATC you need to know the rules, understand the rules and be able to apply the rules. Each of those three aspects builds on the previous one, so remove the understanding and you'll struggle to apply the rules correctly.
No OJTI worth their salt would have a problem explaining anything and helping you to check it out for yourself in the relevant documents. Also, don't accept the reasoning that "we've done it that way since before you were born, lad" - it simply doesn't cut it. If your OJTI refuses to help you check or gets annoyed with you not simply accepting their point of view, get another one before you waste any more of your training time. Imagine being asked on your board why you did something or other and the only answer you could give was "John said so". Your examiner will be inking his FAIL stamp before you've finished speaking.