From recollection, the first longhaul departure has a report time of about 0630. There are many shorthaul 'first wave' reports before 0700, probably in the ratio of 15:1 SH:LH.
If you extend the analysis to 1200 hrs local, this ratio probably increases to about 20:1.
Add to this the number of early inbound flights from Europe linking to outbounds and the ratio of SH:LH probably increases further.
So, what does this mean? Well, I interpret this as putting SH (Eurofleet) as putting their necks on the line for their (better paid) LH colleagues.
A further rough analysis:
Lets say 11,000 LHR cabin crew; 9,000 LH and 2,000 EF. 3 days of strikes.
Over the 3 days of the initial strike, probably 1500 EF will either report or be scheduled to transit LHR - and therefore be expected to strike - so about 75% exposure rate.
Over the same 3 days, probably 1500 LH crew will report - so about 17% exposure rate.
Whichever way you look at this: BASSA are feeding the Eurofleet fodder into the flames to protect Worldwide T's&C's.
Why didn't they call the dispute to start from 1800 local time? Why, because that affects the lucrative LH departures to SIN, BKK, HKG, GRU, JNB, CPT etc.
It really is about time some people did 'wake up and smell the coffee' - to coin an oft (mis)used BASSA phrase.