Hi and welcome to LB, hope you will both enjoy your time here and also gain lots of info and help if you require it.
I have some very unusual ideas about foals and headcollars, so I'm sure you will get other suggestions as well! Is there a reason why you actually need to headcollar this little chap? We never headcollar our foals until they are weaned (told you I was strange. LOL!!)
We do exactly what you have been doing (except we can start a bit earlier as our foals are born here), lots of taking the time for the foal to relax and approach, then come the stratches, (we are still crouched down at this stage). Later we do scratches when the foals approach while we are standing upright. Foals have little or no fear if you dont frighten them in the first place, so very soon we are walking the fields/paddocks with a long line of foals following us, all wanting us to stop and play or give more scratches. We often sit in the field and let them come sit on us, roll on our laps and generally get to know us. We worm and quietly trim all feet during field playtime, and still dont headcollar.
Once weaned, they still look to us for food, games and scratches etc., so once they have settled down without their Mommas, we just pop headcollars on and off as part of the usual game time. Headcollars on and we walk round the field followed by the foals or one foal if that is what we want. Rope on, more walkies, foal following along, no hastle. Next in a stable or smallish enclosed space we show the foal the 'feeling' of a rope stopping and starting them - even this never seems to bother them, all part of human games!
Last April we still hadn't headcollared our last year's fillies. Within 4 days all 5 of them were leading individually all round our farmyard, past tractors and machinery and quietly moving vehicles, loading up and down the steep ramp of our lorry and being introduced to walking in the stream. No problem!! I did warn you I had 'funny' methods! LOL!!
I'm sure other folk will give you good advice on more convential methods, but always remember there is no rush, and the more time you can spend gaining your little fella's confidence and trust (with play and games) then the easier it will be to headcollar him without any stress.
Good luck!