HI, I feel your pain and frustration. this is a lengthy reply!!
Your physio is not taking you for a mug. Essentially boots (hiking, work boots etc) are not suitable for hard track/bitumen walking and you're not the first person to develop achilles tendinopathy doing this (i have done this also - and i'm a physio- i knew better but did it anyway!).
Firstly ultrasound. The basis for this treatment is that it essentially vibrates the cell membranes (with the ultrasound waves) to speed up the metabolism which in turn can improve healing, increase metabolite exchange (bad stuff out and good stuff in). It may feel warm but should not be hot (microwaving you from the inside is not the plan!) or painful/burning etc.
Secondly Friction massage - the theory here is that if you tipped out a box of matches onto a table they'd be everwhere but if you kept rolling your finger back and forth over them in the general direction of across the matches then they would eventually all line up... this is the theory applied to the collagen fibres in tendons and if they are inflamed/torn the body tries to heal the area by laying down new collagen, and if there is a tear then the fibres are every which way, so frictions across the fibres are to try to align the fibres in the "right" direction.
So now we get onto your ongoing problem. it would be best if you did have a pair of shoes (not boots) that did not sit around the achilles area at all or at the least, like a good pair of sneakers, are well padded and soft here.
then you also need to be doing some eccentric heel drops off a step (ask your physio) as these will encourage healing with strength in the tendon. They do hurt. they will make you feel worse before better but that's ok because they work. The eccentric exercise is controlling your body weight descent against gravity. The achilles tendon is a tendon within a sheath - an outer casing which helps the tendon slide up and down when the calf muscles contract (ie. like a piston inside a cylinder where the cylinder is the sheath, there's a bit of lubricating fluid, and then the tendon which moves inside the cylinder). in cases of ongoing achilles tendinopathy there are small blood vessels and nerves that grow into the outer layer of the tendon from the sheath (they're not meant to be there) and cause ongoing pain with movement and perpetuate the irritation because they stop the tendon sliding freely within the sheath. the eccentric exercises will tear these blood vessels and nerves away (this is a good thing) but that's why these exercises will initially be painful. then your tendon should be able to restore normal movement within it's sheath and the muscles are strengthened then the chronic irritation should settle. This can take a few months. you can also use local topicalanti-inflammatory creams (eg. voltaren = diclofenac sodium) either by applying a few times a day or putting a dolop on and covering it with plastic wrap and leaving it overnight. but these are NOT meant to be used long term.
So essentially. see your physio, do your eccentric exercises, get some better non-irritating shoes and your problem may take time but should settle.
good luck
msk101