That's really interesting (particularly as we're both Scots but from different areas). I can't say I have noticed any differences in this before - apart from in the pronunciation of 'r'. But /tr/ for me is made with the tongue firmly on or just behind the alveolar ridge (nowhere near the front teeth) and /tʃ/ as in church is further forward (not as far forward as to be on the front teeth), but that's because the tongue slips further back to where I make my 'r' as in really (way back from the aveolar ridge).The sound you are making requires you to place the tongue a little behind the front teeth instead of touching them. Perhaps this is common in your region - I haven't noticed anyone doing this before, and I don't do it, so I can only assume it is not very widespread.
I would rather surmise he realizes /tʃ̬/ as[tʂ̬] (s with a hook at the lower left side, i.e. retroflex; just in case the diacritics don't come through properly on your browser).The sound you are making requires you to place the tongue a little behind the front teeth instead of touching them. Perhaps this is common in your region - I haven't noticed anyone doing this before, and I don't do it, so I can only assume it is not very widespread.
Thank you. That confirms my surmise.When I pronounce the ch in isolation, I could feel the tip of my tongue slightly tap the ridge at the top front part of my mouth or at least pointing in that direction. Therefore I guess my tongue did slightly bent upwards. What I dod notice is that my tongue kinda fattens up a bit.
I like your answer and have been reading to see if anyone hit on this. The ch sound occurs when rolling the tongue back from t to r (also the case of d to r sounding like jr) rather than disengaging from the top of the mouth and then reengaging for the r sound. I am surprised to hear that so many people don't think this is common. This is how I believe most people from Connecticut in the US speak and I have been told by many foreigners that unlike many Americans, people from CT don't seem to have an accent and are easy to understand.The location where we put our tongue to make 't' and 'r' sounds are far away from each other in our mouth. If you want to clearly say them one after another you have to speak slowly so that your tongue will have enough time to go from the location of 't' sound to the location of the 'r' sound. If you want to speak fast, that is the behavior of every casual speaker in every language, in this case tongue will not have enough time to go the 'r' location right after the 't' and will stay between of two, that is the ch sound.