The storage of forge points on the forge point bar with Forge Plus is an increase from the standard 100 to 1,000. The inability to purchase forge points when having 10 or more forge points has not changed. You will still need to have 9 or less forge points in your bar to purchase forge points with coins or diamonds. Forge Plus only changes the amount of forge points you can manually collect up to.
I have OOS issues so not having to click all over city to collect makes my life less painful, also no searching for incidents as they are all collected in one hit.Why not just use the 5 diamonds to collect your forge points - and manage your bar accordingly. And, you will get all of them on the bar.