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

t=int(input())
for _ in range(t):
    n=int(input())
    l=list(map(int,input().split()))
    key=1
    for i in range(n-1):
        if(l[i]!=l[i+1]):
            key=0
            break
    if(key==1):
        print(-1)
    else:
        k=max(l)
        for i in range(n):
            if(l[i]==k):
                if(i<n-1 and i>0):
                    if(l[i+1]<k or l[i-1]<k):
                        print(i+1)
                        break
                elif(i==n-1):
                    if(l[i-1]<k):
                        print(i+1)
                        break
                else:
                    if(l[i+1]<k):
                        print(i+1)
                        break
            else:
                pass
