A single fighter being able to immobilize an entire fleat has ZIP to do with vector movement. :rofl:
You can just allow a breackthrough if the holding line is too weak (more or less like the overrun rules many wargames have).
Let's add to rules, as an example:
'if you have a 3 to 1 ratio in battle line, extra ships may breackthrough and fire the reserve. The ships making the breackthrough must be the ones with more agility of the fleet'
or something like this.
Also, ratio can be of ships, tonnage, batteries, points given by ship class (1 BB=5, one CA/BR=3, 1 CL=2, 1 escort=1, 10 fighters=1, etc...), or anyway you like.
This way a single fighter won't stop a 20 CAs fleet from attacking the reserve, nor will a single escort.
Also, the most likely ships to be able to breack to the reserve are fighters, something (IMO) not far from what could be in reality. Also guives an advantage to BBs over BRs that can help explaining its continued existence
As example of this rule, imagine a transport comboy escorted by 2 DD atacked by 2 Azhanti class CA. Of course the DDs try to hold the enemy while the transports are held in reserve. As the 2 CAs are worth 6 points and the 2 DDs are worth 2 (3 to 1), the CAs can hold them while the fighters (80 per CA, for a total of 160 IIRC) charge to wreak havock among the transports...
PS all numbers (ratios, class points, etc) are just taken from my hat without real pondering, just as examples. If somwhat like this rule is taken seriously, they should be tested and agreed.