"Our problem lies with the home performances and it is something we have to put right," he says.
"This is a crucial game but it is a mystery to me why we can't seem to get it going at home.
"We're looking comfortable away and, with the crowd we've got and the size of the stadium it shouldn't be hard to do it at Upton Park.
"We may still be suffering the effects of the West Brom game and we're doubting ourselves; I have seen players I expected to play well not doing so and that is our biggest worry at the moment.
"We need strong players and we need to work on their mentality; the bottom line is that, with the money earned here, we have let our supporters down.
"It is a tough game, make no mistake, against a good side, but we are looking to get that home form going.
"We have only won five at home - and we must improve on that because I'm still aiming to win this league."
Alan knows that the supporters' patience is not in never-ending supply and adds:
"They have been patient but they won't be as patient if we keep losing at home - the ball is in our court.
"There is always going to be pressure playing for West Ham - it is a big club.
"But the players we have are well paid to be able to produce."
Alan is pleased that Christian Dailly has made a full recovery from pleurisy, and says:
"It is a bonus to have Christian back, he is an ideal replacement, although we are disappointed to lose Tomas.
"They have got an outstanding player in Fuller and we will obviously have to keep an eye on him.
"They are a good passing team and it will be a good game."
Have Preston, just a point below West Ham in the table, exceeded expectations this year?
"I don't think so; if you look at their squad they have got some very good players there," says Alan.
"They took time to get going under Craig Brown, a new manager with new ideas, but they are doing well now and it will be a tough call for us."
A win would give West Ham the first 'double' of the season and Alan says:
"It is nice to get that; it was a good win on the first day and hopefully we can replicate that."
Although Brian Deane returns, Alan is also hoping that fellow striker Neil Mellor can make a contribution to the second half of the season after he set up the first goal at Wigan on Saturday and played 90 minutes of a reserve team friendly at Crystal Palace in the week.
"It was a good workout and Neil Mellor played very well so that was pleasing; he is a really nice lad," he says.
"He started well then had a bad injury which he picked up in a reserve game but he is over that now and we can get him up to speed for the latter part of the season.