Stay away from above the vents .
However if it's a house converting from your Trad days then they should be relatively clean frames .
I sometimes clean above the vents on a house each day. , therefore always keeping Upto a good standard of frames being really clean .
The house I choose on a daily basis , I will clean all the upside frames first , then go back to the first window , and then clean the windows .
Can't leave above the vent for ever