FD
I fly Airbus A319/320/321 for a 'large' LHR operator, so we fly similar aircraft when it comes to fuel requirements!
I take your point re independent runways vs intersecting runways, but honestly if you operate ex PRG, they barely intersect in that it virtually impossible to think of an incident that would take out sufficient of both runways to preclude landing on 31 or 24.
You say you use LHR with MAN diversion into the UK. Why? You have Cat3 capable Stansted, Gatwick, Birmingham much closer, plus many others. And you take 30 minutes holding fuel?
OK, I know that LHR can be difficult - I have operated in and out as my job for over 15 years and still can't guess what the delays will be - if any, but am (generally) happy with my company policy of 99% statistical contingency fuel, which can give just 10 minutes contingency plus (unrealistic) div fuel, leaving me trip + reserve + about 25 minutes fuel total.
When I joined, then skippers targetted landing a 737-200 with 4 tonnes into LHR as a comfort margin - about where your company is now. Today (a nice day) we were planned into LHR with 2.1 tonnes remaining at midday - I was happy. Why? Well it was certainly a better than 99% day with CAVOK conditions, light 5000 ft winds (which affect the arrival rate), a weekend non peak time arrival.
Re FRA, PRG:
I have never held into PRG, so I would be happy to depart with Reserve + Cont + Div, so on a nice day minimum fuel 100% of the time. Add to that an extra approach + wx factor if TS
around.
FRA: different to PRG - a busy airport which can result in up to 30 miinutes holding (max) on occasional days (high winds when 18 can't be used for departure, for example) at peak times. Have diverted from FRA more than once! Can be long RNAV approaches not always properly factored in to the plog. Generally happy with plog fuel + 15 minutes.
Beware also ZRH and NCE, the only other places in Europe where holding is likely. In ZRH the evenings can cause 30 minute delaysdue runway configuration issues [grrrr] and at NCE protracted low level vectoring on the Saleya approach burns fuel very quickly [90 nm to go when at 3000ft!].