I agree with your comments here in terms of phasic flow only being useful for CFV. also like to see respiratory variation.
The distal FV is always challenging in larger patients.
I use a convex array transducer which gives me much better image quality and you can push hard on it without causing pain. If you use colour Doppler with the convex you should be able to se flow easily in large patients. Keep the sector width narrow and the colour box small. Low PRF and high colour gain. Augment the cold and you will see good colour filling. With a convex you cannot steer the box, but you don’t need to anyway as there is a nice natural Doppler angle to work with.
Another thing I do with the compression technique is to use my other hand and compress the vein from the poster-medial aspect of the thigh using my hand while also compressing from the anterograde-medial aspect with the transducer.
Also look at your acoustic window. If the sartorius is nice and black you can use it effectively but sometimes it is echogenic and a poor window. If this hapens I take the transducer more medially and use the vests medals muscle belly as an acoustic window.
Steve