1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

tests = int(input())
for t in range(tests):
    n = input()
    ls = list(map(int, input().split()))   
    if len(set(ls)) == 1:
        print(-1)
    else:
        maxi = max(ls)
        prev_maxi = False
        for idx,item in enumerate(ls):
            if item == maxi:
                if not prev_maxi and idx!=0:
                    print(idx+1)
                    break
                if idx == 0 :
                    prev_maxi = True
            else:
                if prev_maxi:
                    print(idx)
                    break
                