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

rn=lambda:int(input())
rl=lambda:list(map(int,input().split()))
rns=lambda:map(int,input().split())
rs=lambda:input()
yn=lambda x:print('Yes') if x else print('No')
YN=lambda x:print('YES') if x else print('NO')

for _ in range(rn()):
    n=rn()
    l=rl()
    if len(set(l))==1:
        print(-1)
    else:
        m=max(l)
        for i in range(n):
            if l[i]==m:
                if (i<n-1 and l[i]>l[i+1]) or (i>0 and l[i]>l[i-1]):
                    print(i+1)
                    break