I feel the reason why your therapist is using that frequency is because he/she is aiming for superficial heating to avoid heating the bone during, and also because your condition is a longterm one...setting at 50% should give safe but adequate pulsed heating.

I dont see why you cannot use a 3MHZ, set at 0.7W, with a shorter pulsed duration (say 20%) but increase the frequency of use in a day...if you are considering safety...

this setting will not give the intense heating you get at the clinic but when used often in a day, the effect can be same....

or just use a 3MHZ, set at 0.5W, set at 50 used for 5minutes? or use 3MHZ, set at a higher intensity (1.2W/cm2) at 20%, used for 1min-2mins,

I dont feel there is a rule that restricts you to the setting you are used to...

the aim would be to avoid heating the bone when treating, and being such a superficial tendon the 3MHZ is ideal...frequency of use in a day, length of time of treatment, intensity, and pulsed setting can be adjusted to increase safety while achieveing safe superficial heating

Discuss with your physiotherapist for a protocol to use this at home...

cheers