Ask them - they should able to give you an idea! When my son did his UCAS form earlier this year, I called up the departments saying that their grade requirements may be a bit "of a scretch" and would my son be wasting a choice by putting that course/ uni as one of hos 5 choices. They know what grades they went to over the previous couple of years/ what was in clearing and may be able to steer you accordingly.
One very helpful admissions tutor advised along line of ..." oviously we can't guarantee, but in the last 2 years you would have got in with Grades XXX " My son's predicted grades were lower than all of the AAB/ ABB unis that he applied for and he got 4 offers. All were are the advertised requirement, but at least it gave him something to work for.
He didn't get his firm but traded up from his insurance in clearing and is off to Cardiff in the week.
Next year could be a bit different but possible not as many deferrals as originally anticipated.
Obviously this strategy is less likely to apply to any heavily oversubscribed courses so will vary for subject to subject.