We have 3 phones, two old Vodaphone not smart but basic and one Virgin iPhone 5s. Both Voda get a reasonable signal. I only have to move to the edge of the estate on Timperley Way to get a better signal on the iPhone and it is OK at Morrisons car park just down the road. There appears to be a dead spot which does not show on the theory maps. Have reported this several times but no one investigates on the ground.
If there is a dead spot, as you mentioned, then I don't think a lot can be done about it. This is particularly evident when you only have to walk to the edge of the estate as you'd still be connected to the same mast.
If the Vodafone handsets have "reasonable" signal then this could further indicate a poor reception closer to your property. Keep in mind they operate their own masts so a difference will be seen.
Have you tried manually selecting a network? To do this follow:-
Settings > Carrier > Turn off automatic > Select Virgin
No real difference outside. Can even get a difference indoors depending which way I face. I am just on a dead spot that your maps can not show because you do not actually measure signal strength but use geography to make a theoretical map.