At home you are most likely in your comfort zone, so your level of adapting to the situation while under the influence and the level of judgement necessary isn't as high.
When you are the the pub you are being bombarded by random stimulus, others conversation, different lighting, etcetc, so the amount of information you are receiving and must interpret is much higher, and so you may be more aware of your level of coherence.
For scientific reasons, I request that you go to the pub and drink what/how you would at home, and see if you don't feel much more sloshed.