That's the broad logic with one twist - the strategy is to move to the right somewhat to attract more moderate tory voters in marginal constituencies. It's basically 'gaming' the FPTP system. So you only have to attract say 50,000 tory voters total but if you attract the right 50,000 tory voters that may cause say a 30 seat swing between tories and labour, which is enough to get them back into power.
What I find completely strange is there's no idea/tactic evident to try to attract anybody who didn't vote last time, which is 40% of the available votes. In five years time everyone who is currently 13 or more will get to vote and we'll probably have lost a roughly equal number of the elderly. Attracting that young population could be equally as powerful a tool as attracting marginal voters but they don't seem to be making any public efforts to do so at all and reports suggest Corbyn's campaign is attracting large numbers of new or soon to be voters.
They've also basically taken every labour voter in England for granted - they're just assuming none of them will walk away if they move to the right.
I find the PLP's tactics perplexing to say the least. It seems possible to me they've become obsessed with the 'micro management' of marginal constituencies, fixated on the minutae. It's like a golfer becoming fixated on working on getting his putting technique just right while ignoring the bit about getting the ball onto the green.