Thanks for the clarification Sandy.
I'm not a chemist and it took me a couple of hours to digest everything that was discussed here. I made following tests today with the results:
1. I added sodium bicarbonate into my hypo;
2. I made test strips with
a) 1 layer of sensitizer,
b) 2 layers of sens.,
c) 1 layer of sensitizer with citric acid added,
d) ditto as c) but 2 layers
all were exposed for the same length of time, although c) and d) might've received more exposure because citric acid as a contrasting agent usually requires longer exposure.
3. I fixed for 1 minute and in that time no bleaching was visible
b) very good, beautiful colour but not perfect contrast
c) poor but with better contrast than a)
d) very good contrast but awful colour (dark mustard); in this case the fixer didn't change the colour almost at all
Different papers may react differently, which is a matter of further experimentation.
Thanks everyone for the very interesting, motivating, and helpful discussion!
PS: Happy New Year!