For download, yes, but not the upload, which I care about just as much.
Would anyone know if the ability to only aggregate B32 with B20 is a limitation of my device (B535-232), or is it a limitation of Three (or my particular mast) ?
Bit of both,
Three UK has bands 28, 20, 32, 3 and 1, or 700mhz, 800mhz, 1400mhz, 1800mhz and 2100mhz for 4G
Band 32 is only ever used as an aggregate band by 3 UK, and the B535-232 can only aggregate it with Band 8 or Band 20, and 3 UK does not offer Band 8.
A 3CA device would be able to aggregate band 3+ band 20+ band 32, or band 1+ band 3+ band 32 or band 1+ band 20+ band 32.
Vodafone UK can aggregate Band 8 + Band 32.
The other issue is the B535-232 can only aggregate certain bands on upload:
UL CA: 1C , 3C , 7C , 38C
Up Load Carrier Aggregate on 3 UK using the B535-232 is limited to Bands 1 or 3, and for whatever reason the B535 is limited to uploading on the same band it has chosen for primary download.
Where to go, either try a different mobile network, or look for a more powerful device, cat12 as a minimum would be my suggestion.