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

for i in[0]*int(input()):
    #for j in [0]*int(input()):
    n=int(input())
    lis=list(map(int,input().split(' ')))
    if len(set(lis))==1:
        print(-1)
    else:
        m=max(lis)
        for k in range(0,n):
            if lis[k]==m and (lis[k-1]<lis[k] or lis[k]>lis[k+1]):
                print(k)
                break