Keep wine bottles horizontal, And in the frig?
Keeping wine bottles horizontal preserves the cork and keeps the seal secure. If you leave a wine bottle standing, it may lead to dried out corks and air getting in which will ruin the wine.
Other things that stored wines like are; low light, moderate temprature, and higher humidity.
Keeping opened bottles, including reds, in the frig will keep the wine drinkable longer.
There are times where the wine rack is filled and there's no where else to store your wine horizontally. The answer of course is to buy another Modularack USA layer or row for your wine rack and for your ever expanding wine collection.