Storage limitations

[mrm27]

I live in England and this summer it was extremely warm by our standards (weeks in the high 80s and low 90s). The cupboard under the stairs, where I keep my wine, got very warm, despite being well sheltered and temperatures in there regularly reached 80-85 degrees. Some of the reds went distinctly off, but the sweet whites, notably an eleven year old Sauternes, survived well. There was considerable seepage, but one piece of advice I got about that was to stand the bottles upright, to prevent the wine expanding along the cork and hitting the air. Is this bad advice?